Trimmer condenser



Nov. 15, 1966 F. w. EDWARDS 3,286,139 TRIMMER CONDENSER Filed Sept. 2, 1965 1N VENTOR. 5750 W. fax/4 4 05 United States Patent Office 3,286,139 Patented Nov. 15, 1966 3,286,139 TRIMMER CONDENSER Fred W. Edwards, Park Ridge, 11]., assignor to Standard Kollsman Industries, Inc., Melrose Park, Ill., a corporation of Illinois Filed Sept. 2, 19,65, Ser. No. 484,561 9 Claims. (Cl. 317-248) This invention relates to trimmer condensers, and more particularly relates to novel trimmer condensers incorporating arelative'ly high minimum capacity setting.

In many situations requiring the utilization of a variable capacitive circuit element, it is necessary to provide controlled temperature compensation. The mechanical requirement imposed by the variable section have, however, required the utilization of materials which do not have the desired degree of temperature control, with the end result that intricate and expensive auxiliary means must be employed to maintain proper circuit performance over the experienced temperature extremes. Further, for high frequency operation, it is desirable to provide a structure having a minimum of inherent inductance. The instant invention avoids these problems in an extremely simplified manner by the provision of a condenser assembly having a fixed capacitive section to provide a minimum value, and a variable section, additive thereto. The fixed section may be constructed of a wide choice of materials, such that it is either predominant in its temperature characteristic or suitably compensates for the characteristic of the adjustable section.

In accordance with the present invention, I provide a disc of ceramic, or other suitable dielectricmaterial, having a central opening forming a toroidal shape. This disc is rendered capacitative bysuitable metallic coatings on its opposed faces. Such disc condenser is utilized here in to establish the minimum capacity value for the trimmer condenser. Extending from one face of such disc is a hollowed cylinder or tube of a suitable ceramic or other dielectric material. The outside surface of the cylinder is metal'lized to constitute a plate of the condenser. A threaded memberis arranged to. project within the toroidal disc and cylinder to alford an adjustable capacitance with the tubular metal layer. Thescrew, threaded to its minimum or exterior position wi-th respect to the cylinder, leaves the stated minimum capacity due to the disc condenser of the trimmer.

The mechanical characteristics of ceramics are such that the fabrication of a threaded cylinder for use in a trimmer of this type limit the materials available to a narrow range of electric characteristics while the disc can be readily fabricated from a wide variety of materials so that this provides an adjustable condenser availability by designing in such a way that the fixed minimum condenser section is either predominant in its temperature char acteristic or compensates forthe characteristic of the adjustable section.

The primary object of the present invention is to provide a novel trimmer condenser of minimum inherent inductance having a fixed minimum capacitance section in conjunction with a variable capacitance. section.

Another object of the present invention is to provide a novel trimmer condenser having controlled temperature characteristics.

A further object of the present invention is to provide a novel trimmer condenser composed of a disc shaped condenser section which constitutes a minimum capacitance for the trimmer, and a tubular extension condenser which constitues a variably adjustable added capacitance section.

Still another object of the present invention is to provide a trimmer condenser having a high minimum capacitance constructed relatively at low cost and having a minimum inherent inductance.

These and further objects of the present invention will become more apparent in the following description of an exemplary embodiment thereof, taken in connection with the following drawings, in which:

FIGURE 1 is an elevational View of the trimmer condenser of the present invention.

FIGURE 2 is a plan view of the condenser disc, as seen along the line 22 in FIGURE 1.

FIGURE 3 is a plan view of the condenser disc, as seen along the line 33 in FIGURE 1.

FIGURE 4 is an enlarged exploded illustration of the invention trimmer condenser.

Referring to the figures, trimmer condenser comprises a cylindrical tube 5 1 of ceramic or other suitable dielectric material. The exterior surface of cylinder 51 is coated with a closely adhering metallic layer 52, such as silver. The silver coating 52 extends from the bottom edge of cylinder 51 to a location 53 near its upper end. The interior of cylinder 51 is hollow to receive a metallic member which is adjustable axially along the cylinder 51 in a manner to be more -fully described.

'Secured with cylinder 51, at its base, is a disc 55 of dielectric material, such as ceramic, and which constitutes the high minimum capacitance for the condenser 50, as will beset forth. FIGURES 2 and 3 show respective opposite' faces of the disc 55, and the central opening 56 thereof. The upper face, or cylinder-side, of disc 55 contains an annular metallic coating 57 of silver. Annular layer 57 is soldered to layer 52 of cylinder 51 along soldered joint 58. The combined metallic layers 52, 57 constitute one plate or section of the trimmer condenser 50. Lead 60 connects to cylindrical metallic layer 52 for external connection of condenser 50, circuitally.

The bottom face of disc 55 is coated with annular metallic layer 61, also preferably of silver. The layer 61 coacts capacitive'ly with the annular layer 57 on the opposite disc face. The layer 61 is secured with bracket leg 62, mechanically and electrically. Alternatively, layer 61 may be placed directly against the unit chassis (not shown) in which it is utilized, with such mounting being typical where layer 61 is connected to chassis ground. The indicated bracket is L-shaped, and contains extending arm 63 used to mount the condenser assembly. The bracket '62 constitutes the opposite terminal of the condenser 50 to lead 63. As a-nnu'lar layer 61 is juxtaposed with bracket arm 62, the capacitive action of the combi nation, in conjunction with opposite annular metallic layer; 57 constitutes the minimum capacitance for the trimmer condenser 50, as will be now understood by those skilled in the art.

While the effect of the vertically extending cylindrical layer 52. adds some minorcapacitive value to the minimum for the trimmer condenser 50, the basic minimum capacitance is afforded by the annular layer 57 on doughnut 55 with respect to layer 6'1. Such minimum capacitance is thereby provided with a minimum and negligible inherent inductance. The purpose of the cylindrical layer 52 is primarily for affording the net adjustable capacitance to which the condenser may be set, above the said minimum capacitance, as will now be set forth.

Towards this end a threaded metallic member, which is threaded screw 65, is arranged to axially extend through the interior opening 56 of the disc 55 and into the hollow portion 66 of cylinder 5, to variably coact capacitatively with cylindrical layer 52. The threaded screw 65 coacts with interior threads 67 (see FIGURE 4) of the nut 68 which is secured with leg 62 of the bracket. The head 70 of screw 65 is notched for screwdriver adjustment of the trimmer capacitance. The axial position of screw member 65 within cylinder 51, and with respect to cylindrical coating 52, determines the additional capacitance for the condenser that is superimposed upon the stated minimum capacitancethereof. The interior position, indicated in solid lines in FIGURE 1, of screw 65 illustrates such intermediate trimmer capacitance value setting for condenser 50.

The farthest position of adjustment screw 65 into cylinder 51 determines the maximum capacity setting for the trimmer condenser. The minimum capacity setting, which corresponds to the stated minimum capacitance for the trimmer condenser 50, is indicated at the extended position 70 in dotted lines FIGURE 1. In such position 70, the threaded portion of screw 65 engages with nut 68, and is in the preferred embodiment in the minimum coaction position (almost negligible) with cylindrical coating 52. Such representation of the minimum capacitance is determined by the condenser action basically of the silver coated doughnut disc 55 as stated hereinabove.

FIGURE 4 is an enlarged exploded view of the invention trimmer condenser 50, affording a clearer understanding of its component sections and assembly thereof. The metallic nut 68 and annular metallic coating 61 are soldered or otherwise mechanically and electrically atfixed to the metallic bracket arm 62. An opening 71 is arranged in bracket arm 62 through which screw 65 passes. The diameter of opening 71 is preferably larger than the internal opening of disc 55 at 56; the interior circumference 72 of annular conductive layer extends interiorly from the periphery of opening 56; and the interior circumference 73 of the opposite annular layer 57 (see FIGURE 3) is inwardly spaced from the periphery of opening 56 'of disc 55. This serves as a clearance spacing to isolate equi-potential conductive film 57, solder fillet 58 and conductive film 52 from voltage breakdown with opposite condenser terminal film 61 (or screw member 70, nut 68 or bracket 63, electrically connected thereto).

To maintain the conductive portion of disc 55 spaced safely from screw member 65 which passes therethrough', the distance between the circumference of the disc opening 56 and the inner periphery 73 of annular conductive layer 57 (as shown by d in FIGURE 3) is preferably of the order of the thickness between the wallsof the cylinder 51. In this manner, the outer cylindrical layer 52 on cylinder 51 still readily is secured electrically and I mechanically with the annular layer 57 by a ring of solder 58.

A simple practical trimmer condenser, with the stated electrical characteristics, is accordingly afforded by the invention condenser 50. It is relatively inexpensive of component fabrication. In preferred production thereof, the cylinder 51 and disc 55 are suitably silvered with metallic coatings 52, 57 and 61' already described. The cylinder 51 and disc 55 are assembled in the manner shown in FIGURE 1, together with bracket 62, 63, nut 68 and screw 65. A preformed ring of solder, containing suitable flux, is arranged at the base of cylinder 51, where it is contiguous with the annular silver layer 57 on'disc 55. Similarly, solder and flux are arranged for surface- 61 adjacent bracket leg 62, andfornut 68. The thus assembled components are thereupon subjected to heating for the soldering phase of assembly. The terminal 60 may be incorporated with assembly 50, or thereafter as desired, for the utilization of the condenser.

As stated, condenser 50 has a minimum inherent inductance value for the capacitance range for which a given condenser 50 is constructed. In a particular embodiment, wherein the disc 55 had an inner diameter of 0.130 inch, and an outer diameter of 0.360 inch, and a thickness of 0.070 inch, the nominal minimum capacitance was 10.6 picofarads. The cylinder 51 of this condenser embodiment had a diameter of 0.18 inch, and an axial length of 0.3 inch, with a capacitive range for the trimmer condenser 50 to a maximum of 13.8 picofarads. Disc section 55 may be constructed of titanium dioxide while the mechanicalrequirements imposed by cylindrical section 51 are more readily met by a material such as Steatite. These materials have been selected so that the temperature characteristics of disc section 55 will be either predominant or compensate for the temperature characteristic of cylindrical section 51.

It is to be understood that specific dimensions and materials of the invention condenser will provide different minimum and maximum capacitance ranges and the above parameters are given for illustrative purposes only and are not intended as a limitation of my invention. While the present invention has been described in connection with an exemplary embodiment, and in a particular application, it is to be understood that modifications may be made both as to its construction and application without departing from the broader spirit and scope of the invention, as set forth in the following claims.

I claim:

1. A trimmer condenser including a first and second terminal, a fixed capacitive section and a variable capacitive section electrically connected between said terminals, said fixed capacitive section including a disc with first and second metallic layers on opposed faces thereof, said variable section including a tubular member having an external metallic layer electrically connected to said first disc layer, said tubular layer electrically connected to said first terminal, said second disc layer electrically connected to said second terminal, means for adjusting the capacitance of said variable section such that the combined capacitance of said fixed and variable sections, as presented to said first and second terminals, is adjustable. V 2. A trimmer condenser as set forth in claim 1, characterized as having relatively low inherent inductance,- said disc and first and second metallic layers constituting substantially the minimum capacitance value of said condenser.

' 3. A trimmer condenser as set forth in claim 1, wherein saiddisc is formed of a first dielectric material, said tubular member is formed of a second dielectric material, said materials of pre-selected temperature coeflicients such that the temperature characteristic of said disc predominates.

4. A trimmer condenser as claimed in claim 1 wherein said adjusting means comprises a metallic element adjustably positionable in said tubular member to preset an extended capacitance value for the condenser.

5. A trimmer condenser as claimed in claim 4, further including means for operatively maintaining said element in its preset position. 6. .A trimmer condenser as claimed in claim 4, further including a bracket connected with the other of said disc layers, and means secured with said bracket for maintaining said element in its preset position.

7. A trimmer condenser as set forth in claim 2, wherein said adjustment means comprises a metallic screw adjustably positionable in said tubular member and connected to said second disc layer to preset an extended capacitance value for the condenser.

3,286,139 5 6 8. A trimmer condenser as claimed in claim 1, in which References Cited by the Examiner said first disc layer is annular in shape and extends within UNITED STATES PATENTS a region gap-separated from the inner opening of the disc to minimize voltage breakdown to said second disc layer 3067369 12/1962 Roggon 317 248 via said inner opening. 5 FOREIGN PATENTS 9. A trimmer condenser as claimed in claim 7, in which 2 499 4 193 Germany said one disc layer is annular in shape and extends within LEWIS H MYERS Primary Examiner. a region gap-separated from the inner opening of the disc to minimize voltage breakdown to said other disc layer via LARAMIE ASKIN Exammersaid inner opening. 10 E. GOLDBERG, Assistant Examiner. 

1.A TRIMMER CONDENSER INCLUDING A FIRST AND SECOND TERMINAL, A FIXED CAPACITIVE SECTION AND A VARIABLE CAPACITIVE SECTION ELECTRICALLY CONNECTED BETWEEN SAID TERMINALS, SAID FIXED CAPACITIVE SECTION INCLUDING A DISC WITH FIRST AND SECOND METALLIC LAYERS ON OPPOSED FACES THEREOF, SAID VARIABLE SECTION INCLUDING A TUBULAR MEMBER HAVING AN EXTERNAL METALLIC LAYER ELECTRICALLY CONNECTED TO SAID FIRST DISC LAYER, SAID TUBULAR LAYER ELECTRICALLY CONNECTED TO SAID FIRST TERMINAL,SAID SECOND DISC LAYER ELECTRICALLY CONNECTED TO SAID SECOND TERMINAL, MEANS FOR ADJUSTING THE CAPACITANCE OF SAID VARIABLE SECTION SUCH THAT THE COMBINED CAPACITANCE OF SAID FIXED AND VARIABLE SECTIONS, AS PRESENTED TO SAID FIRST AND SECOND TERMINALS, IS ADJUSTABLE. 